Polyhalogenoaromatic compounds. Part 43. Inter- and intra-molecular reactions of polychloroaromatic compounds with copper

Abstract

The reaction of polychloroiodoarenes with copper in dimethylformamide gives good yields of the biaryls. 4Bromotetrachloropyridine gives products of halogen exchange and reduction as well as coupling. Pentachloropyridine gave only tetrachloropyridines. Evidence against free radical or pyridyne intermediates is presented, and it is postulated that the reactions proceed via pyridylcopper compounds, although an electron transfer mechanism is not excluded. On reaction with copper, some 4-(o-halogenophenoxy)- and 4-(o-halogenothiophenoxy)tetrahalogenopyridines give products of cyclisation, reduction, and halogen transfer. Copper reacts initially, at least in part, with the pyridyl group rather than with the o-halogenoaryl group. The results are again consistent with a reaction pathway involving a pyridylcopper intermediate. The products of nucleophilic substitution in pentahalogenopyridines by some phenols, thiophenols, and anilines are reported.